Manufacture of felted-fiber reinforced abrasive products



Patented Mar. 23, 1954 2,673,146 7 MANUFACTURE or FELTED-FIBER REIN- FORCED ABRASIVE Joseph N. Kuzmick and Lamar PRODUCTS S. Hilton, Clifton,

., assignors to Raybestos-Manhattan, Inc.,

Passaic, N. J., a corporation of New Jersey No Drawing. Application May 9, 1950,

Serial No.

6 Claims. (01. 51-299) This invention relates abrasive products such as etc., and more particularly to such abrasive products which are reinforced by felted cellulosic or other fibres for obtaining maximum tensile and transverse strengths.

The prime object of this invention is to produce abrasive or grinding wheels of a felted fibre structure at a cost comparable to grinding wheels of non-fibrous nature well known in the art.

Grinding wheels of laminated fibres or laminated cloth reinforcement are known. However, their great disadvantage lies in the uneconomical process required to produce them. As an example of the prior art in this field is the laminated fibre wheel constructed by first making a sheet on a Fourdrinier machine from beaten wood pulp or rag stock, which sheet in the form of paper is then coated with a binder followed by a superficial application of abrasive grain; circular disks to the manufacture of abrasive wheels, disks,

an hydraulic press with or without heat at tremendous pressure to form a single laminated unit. The objection to this method is the high cost of providing machinery to accomplish the purpose, the Waste involved in rejecting portions of unused sheet after stamping and the high labor costs involved in laminating such a multiple of sheets to arrive at the desired thickness of the finished product.

Another method for producing a fibre-reinforced abrasive wheel is one wherein medium weight cotton duck or other woven fabric is run through a conventional spreading machine where a thin layer of a pasty composition consisting of .brasive grains and a binder is spread over one surface or one side of the Woven fabric, this being followed by drying the resulting product by passing the same through heated chambers after which these operations are repeated to coat the other surface or side of the woven fabric. Disks are then stamped out from this abrasive coated fabric, and these disks are laminated under heat and pressure to form the desired grinding wheel. To make a typical cut-off grinding wheel by this method requires five plies or laminations of the coated fabric; and it is obvious that the cost of equipment, waste of fabric after stamping out the disks, etc., involves a process and. the making of a product which is beyond reasonable cost.

In order to dispense with the laminations, and with the thought of homogeneously distributing a felted fibre throughout an abrasive body, it has been attempted to make a mixture or a pulpy mass of fibre, binder and abrasive and cast the tribute the fibres for maximum felting requires water to the extent of one part fibre to parts of water, and requires long agitation of this mixto is impractical for the reason that the abrasive grains immediately settle out due to the difference in gravity and the lack of viscosity of the slurry. In order to remedy this difiiculty, an attempt has been made to complete the fibrous water slurry and abrasive in a violent agitator, while adding a binder such as rubber or synthetic rubber latex and coagulate said binder on the fibres and abrasive while in motion, with a consequent separation of fibre-abrasive-bond phase and a water phase, after which the occluded water maximum strength.

We have found that the involved problems of producing a felted-fibre reinforced abrasive product fibrous structure is homogeneously distributed throughout the body of the abrasive product are solved by employing clay such as bentonite in the system, and more particularly, by first mixing the fibre flock with a water dispersion of such colloidal clay, thereby producing a base of a felt-forming viscous and thixotropic mass. The employment in the process of such a colloidal clay as explained hereinafter has been found to provide the solution to the problem and the following advantages thereof:

1. The introduction of bentonite clay, which need only be about 6% of the total water used. provides viscosity to the point of the mass being gelatinous. This viscosity alone solves the problem of securing proper suspension of the abrasive.

2. Th introduction of the fibre flock to the clay-water gelatinous mass and mixin the same results in complete dispersion of "he fibres to the extent that, upon subsequent expelling or re moval of water, a perfect felting of the fibres is achieved, providing maximum fibre reinforcement.

3. The proportion of water in the system is decreased to the extent, that a 6% concentration. or more, of fibre can be introduced to the aqueous system, with consequent perfect felting, as against a maximum of 1% and a normal of of fibre to wa ter ratio which would normally be I of its smaller particle size, provides a clay-rubber final mix of extreme strength and adhesiveness, as it is well known, particularly in the rubber art, that colloidally dispersed fillers provide the maximum reinforcing property for rubber; and, further, this colloidal clay-rubber binder bonds the individual fibre particles which are also perfectly dispersed for maximum felting into a homogeneous mass supporting the distributed abrasive granules into a grinding wheel unit which can be characterized as practically unbreakable.

On the matter of dispersion of the fibres, it may be pointed out that the gelatinous nature of the water-clay mix provides sufficient friction during mixing with the fibre to separate the fibres from their original bundles into individual units, whereas to accomplish the same degree of dispersion would normally re uire 10 to times more water. Also, the thixotropio nature of bentonite clay is such that while in motion in the mixer, it provides the necessary friction and fluidity not only to perfectly disperse the fibre but to distribute the abrasive granules, and also the colloidal binder. On removal of motion and followed by casting into proper sized receptacles, the phenomenon of thixotropy asserts itself by an immediate gelatinization of the mass which permanently suspends fibre, abrasive, etc., into proper position for conclusion of the process.

The following are typical examples of practicing the method of the present invention for Ohtaining the mixes or masses ready for the casting or molding operation.

Example I Pounds Bentonite clay 6 Water 60 Cotton flock 6 The clay is dispersed in the water and permitted to swell for several hours to maximum viscosity. The cotton flock is then added to the water dispersion with thorough mixing.

While the above is being stirred, the following ingredients are added in rotation or sequence:

Butadiene acrylonitrile latex, 40%

Phenolic resin, powdered or dispersed 2 lbs. Aluminum oxide abrasive 48 lbs,

While this example is a typical one used, it may be varied over a fairly wide range of proportions in order to provide wheels of different physical characteristics, such as Wheels of a soft rubbery nature, or wheels of a hard and stiff character as well as intermediate variations of these characteristics.

Example II A typical example of a felted-fibre wheel having more resilient properties is that obtainable with the following formulation:

. Pounds Bentonite clay 5 Water 50 Alpha flock 5 Bentonite clay and water are first mixed to form the dispersion of the clay and the alpha flock 'is subsequently added. To this dispersed fibre is added in rotation:

Butadiene-styrene latex, Dispersed sulphur, 75% Dispersed zinc oxide, 50% Water lbs 30 Aluminum oxide abrasive lbs 50 This mix provides a flexible wheel in which the disclosed binder cures to what is normally known as a soft rubber cure.

Example III An example for an extremely rigid and slower cutting Wheel is as follows, said example being generic:

40 solids lbs 24 solids oz 8 solids oz 4 Pounds Bentonite clay 6 Water 40 Cotton flock 3 Nylon flock 3 Bentonite clay and water are first mixed to form a dispersion of the clay with subsequent addition of cotton and nylon flock. To this dispersed fibre is added:

Pounds Butadiene-acrylonitrile, 40% solids l0 Pulverized phenolic resin 6 Dispersed sulphur, 75% solids 1 Dispersed zinc oxide, 50% solids /4 Water 45 Aluminum oxide abrasive #24 55 The binder in this example consists of a copolymer of phenolic resin and butadiene-acrylonitrile rubber in about equal proportions, which provides a binder of utmost rigidity both hot and at room temperature, and contributes to a wheel with slower cutting but long-lasting properties.

The entire mixing cycle with the exception of the preliminary time allowed for the swelling of the bentonite clay in water is of the order of 10 to 15 minutes. This is extremely fast mixing for the disclosed concentration of fibre and abrasive grains when compared to the fibre water slurry used in the making of paper.

We have found that the most suitable binders to be used in the process are the class of colloidally dispersed rubbers such as natural rubber latex, butadiene-styrene latex, butadiene-acrylonitrile latex, and chloroprene latices. For the fibre we may use any of a variety of fibre flock, such as linen flock, nylon flock, rayon flock, alpha flock and cotton flock. The abrasive grain employed may be of any desired mesh, as from #24 to mesh.

The viscous and thixotropicabrasive mix obs ture in the form of even slight bleeding or ex pelling of the components of the mix in the operation of removing or expelling water has to be guarded against.

To accomplish these 32 F. with subsequent thawmg. The latex binder is thus coagulated into a moderate pressure.

The pressing of the thawed mass in the mold is preferably done with hydraulic pressure applied moved at low temperature drying at 100 F. to 150 F. for eight to twelve hours.

After these steps of coagulation and water expulsion, the product is then cured or vulcanized to its final condition. Curing or vulcanizing may be performed in any of several Ways, and the preferred method for so-called grinding wheels With a recessed center is one wherein the coagulated pre-dried blank is cured. directly in a mold of proper dimensions under heat and pressure in an hydraulic ram press for one to one and a half hours at 330 F. Flat Wheels or disks Where it is unnecessary to change the contour of any portion of said disk, are usually cured or vulcanized between plates, with light clamping pressure to hold the plates parallel, in gas heated or electric heated ovens for 12 to 18 hours at 320 F.

The obtained ceptionally efiicient in their grinding and polishing ability and they provide finishes more in the order of so-called set-up Wheels because of their inherent quality of absorbing shock.

These Wheels or disks can be made in various degrees of stiffness by altering either the sulphur content up or down, the phenolic resin content up or down, and their cutting ability can be varied by either raising or lowering the abrasive content.

The: thin disks used for so-called disk grinding can be made flexible enough to mount on equipment which novv coated disks which are extremely flexible. They can also be made practically rigid where such is the requirement. The rigid type is more adaptable to cutting-off operations where greater rigidity is required for making straight cuts. It is interesting to note that with this maximum rigidity, these cutting-oil disks or wheels are tough enough to Without breakage.

We claim:

1. The method of making a felted-fibre reinforced abrasive product which consists in mixing a Water dispersion of a colloidal clay with a fibre fiocl; and producing a felt forming mass in which the fibres are dispersed in the mass, the concentration oi fibre in the Water being of the order of 6% to 15% and the Weight content of the fibres in the mass being of the same order of magnitude as the weight content of the colloidal clay in the mass, mixing the said mass with abrasive grains. and a binder, including a colloidally dispersed rubber binder, ducing a felted-fibre reinforced abrasive-binder mass, shaping said abrasive mass to abrasive product form, expelling the Water then curing the same.

2. The method of making a felted-fibre reinforced abrasive product which consists in mixing a water dispersion of a colloidal clay with a cellulosic fibre flock and producing a felt forming viscous and thixotropic mass in which the fibres mass, the concentration of fibre in the Water being of the order of 6% to of the fibres in the binder binder, forced abrasive-binder mass, shaping said abra- 3. The method of making a felted-fibre reinforced abrasive product which consists in mixing a water dispersion of a colloidal clay with a fibres in the mass being of the same order of magnitude as the weight content of the colloidal clay in the mass, mixing the said mass with abrasive grains and a binder including a colloidally dispersed rubber binder, thereby producing a felted-fibre reinforced abrasive-binder mass, freezing and thawing said abrasive mass to produce a continuous bonded phase and a discontinuous water phase, shaping said abrasive mass to abrasive product form, expelling the water and then curing the resulting product.

5. The method of making a felted-fibre reinforced abrasive product which consists in mixing a water dispersion of a colloidal clay with a fibre flock and producing a felt forming mass in which the fibres are dispersed in the mass, the concentration of fibre in the water being of the order of 6% to 15% and the weight content of the fibres in the mass being of the same order of magnitude as the weight content of the colloidal clay in the mass, mixing the said mass with abrasive grains, a binder including a colloidally dispersed rubber binder, and a vulcanizing agent, thereby producing a felted-fibre reinforced abrasive-binder mass, shaping said abrasive mass to abrasive product form, freezing and thawing said abrasive mass to produce a continuous 8 v bonded phase and a discontmuous water phase, compressing the mass to final product form and. expelling the water therefrom and then vulcanizing the resulting product.

6. The felted-fibre reinforced abrasive product obtained by the method of claim 1.

JOSEPH N. KUZMICK. LAMAR S. HILTON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,668,475 Wescott May 1, 1928 1,931,428 Boudy Oct. 17, 1933 1,953,983 Benner Apr. 10, 1934 2,301,998 Bernstein et a1. Nov. 1'7, 1942 2,396,907 Volk et a1. Mar. 19, 1946 2,418,282 Williamson Apr. 1, 1947 2,460,367 Sharpe Feb. 1, 1949 2,580,076 Deane Dec. 25, 1951 FOREIGN PATENTS Number Country Date 360,482 Great Britain Nov. 9, 1931 117,723 Australia NOV. 18, 1943 

1. THE METHOD OF MAKING A FELTED-FIBRE REINFORCED ABRASIVE PRODUCT WHICH CONSISTS IN MIXING A WATER DISPERSION OF A COLLOIDAL CLAY WITH A FIBRE FLOCK AND PRODUCING A FELT FORMING MASS IN WHICH THE FIBRES ARE DISPERSED IN THE MASS, THE CONCENTRATION OF FIBRE IN THE WATER BEING OF THE ORDER OF 6% TO 15% AND THE WEIGHT CONTENT OF THE FIBRES IN THE MASS BEING OF THE SAME ORDER OF MAGNITUDE AS THE WEIGHT CONTENT OF THE COLLOIDAL CLAY IN THE MASS, MIXING THE SAID MASS WITH ABRASIVE GRAINS AND A BINDER, INCLUDING A COLLOIDALLY DISPERSED RUBBER BINDER, THEREBY PRODUCING A FELTED-FIBRE REINFORCED ABRASIVE-BINDER MASS, SHAPING SAID ABRASIVE MASS TO ABRASIVE PRODUCT FORM, EXPELLING THE WATER THEREFROM AND THAN CURING THE SAME. 